The Assignee of the present invention manufactures imprinters which are used for making imprints of a merchant's station plate and a credit card onto a formset for recording a credit transaction. Imprinters of this type have an extruded metal base which is made from aluminum and further a carriage which is a multiple piece element, including thermoplastically molded parts, to which are attached first and second rolling platens which respectively imprint the image of the station plate by moving the carriage in a first direction and the image of the credit card by moving the carriage in the opposite return direction. This type of imprinter is known as the double roller, double stroke imprinter in the industry.
FIGS. 1-4 illustrate the current design of the carriage mechanism used in imprinters manufactured by the Assignee of the present invention of the aforementioned double roller, double stroke design. These imprinters have a thermoplastic piece 10 to which are joined a pair of metallic side plates 12. The side plates 12 each contain a pair of axles 14 on which thermoplastically molded wheels 16 are mounted for engaging the lower rails respectively located on the sides of the imprinter. Additionally, the thermoplastically molded piece 10 contains a pair of molded slots 18 which each are defined by inboard wall 20 and the outer metallic plate 12. The metallic plates 12 are attached to the thermoplastic piece 10 by metallic fasteners 22.
The molded slot 18 defined by the inboard wall 20 and outer plate 12 holds a wheel mounting mechanism 24 which rotatably supports a third wheel 26 which is attached to an axle (not illustrated) of the wheel mounting mechanism. The third wheels 26 ride upon an upper rail on the respective sides of the extruded aluminum base of the imprinter opposite to the lower rails on which the lower wheels 16 ride.
It is important that spacing of the carriage with respect to the flatbed of the imprinter be adjusted within a set range. In order to obtain a high quality imprint which is OCR readable, it is necessary that a set range of clearance exist between the rolling platens and the base of the imprinter during imprinting. The wheels which support the carriage on the rails of the base must be adjusted to be spaced from each other within a set range so that unacceptable play orthogonal to the flatbed of the imprinter during imprinting does not exist, which would degrade the quality of the imprint, before the clearance between the rolling platens and flatbed can be set. An initial adjustment of the wheels which support the carriage may require between 0 and 0.002 of an inch of play between the wheels 16 and 26 and the rails (not illustrated) of the base of the imprinter, to permit a proper height adjustment to be subsequently made for the rolling platens carried by the carriage relative to the flatbed to insure that a high quality optical character readable (OCR) image is achieved. The prior art carriage mechanism, including the molded piece 10, sets the spacing between the wheels 16 and 26 and the rails within the aforementioned range by adjustment of screw 28. Turning the screw 28 inward into the top surface 30 of the piece 10 causes the end 32 of the screw to force the wheel mounting mechanism 24 downward to lessen the spacing between the wheels 16 and 26 which reduces the orthogonal play between the wheels and the rails. Turning the screw 28 outward has the opposite effect.
The prior art carriage of FIG. 1 has several disadvantages. In the first place, the molding of the thermoplastically molded piece 10 requires between 20 and 30 seconds because of the thermal cycling required for the molding process which slows the throughput of molding the molded carriage piece when compared to other forming techniques such as metal extrusion which heretofore has not been successfully used in the manufacturing of imprinter carriages. Additionally use of a wheel mounting mechanism 24, which requires attachment to the thermoplastically molded piece 10 and the adjustment thereof to set the spacing between the lower wheels 16 and the top wheel 26 and the rails to the aforementioned set range adds substantial expense to the overall cost of the imprinter. The cost of manufacturing an imprinter is a significant factor in its salability with any appreciable reduction the manufacturing costs of an imprinter with the capability of imprinting clear OCR readable characters representing a significant improvement which will increase sales.
In the prior art imprinters with metallic carriages have been manufactured by various processes. Multiple stage piercing of flat plate has been used. Others, including the Assignee, have used steel strip, which is a flat material, which does not permit internal features to be installed in the part without secondary addition of components requiring additional parts and labor. Such components include assembled roller brackets. More recently, carriages have been made by die casting which provides the ability to form internal features during the casting process which eliminates the requirement for additional parts. However, while die casting has the advantage of providing a complete assembly including internal parts with high dimensional tolerances, it has the disadvantage of being an expensive process.
Previously, the Assignee has used an eccentric mount for the third wheel of the carriage support to set the spacing between the third wheel and the first and second wheels and the rails of the base to achieve the aforementioned set spacing. The eccentric mount was adjusted to vary the spacing between the axle supporting the third wheel and the first and second wheels. Eccentric mounts add parts and labor expense to imprinter cost.
U.S. Pat. Nos. 4,270,453 and 4,281,596 disclose a double rolling platen, double stroke imprinter having a carriage with first and second pairs of inclined slots mounted in downwardly extending sides which support the axles of a pair of rolling platens. For movement of the carriage in a direction in which one of the rolling platens is not imprinting, the slots function to guide the axle supporting the platen which is not imprinting upward so that the lifted rolling platen will roll over the station plate or credit card without imprinting character information onto the formset. However, for movement of the carriage in a direction in which one of the rolling platens is imprinting, the slots supporting the axle of the imprinting platen force the axle of the imprinting platen downward to exert imprinting pressure on the station plate or credit card to imprint characters onto the formset.
The carriage of the '453 and '596 patents transmits the force of imprinting transferred through the rolling platen axles to the top surface of the pair of slots contained within the side walls of the carriage to the bed of the imprinter and to the wheels riding on the base which support the carriage during the imprinting stroke. However, the carriage of the '453 and '596 patents is of a complex shape requiring precise dimensional tolerances to maintain proper spacing between the rolling platens and the flatbed. The clearance between the flatbed and the rolling platens is established by the axles of the rolling platens contacting the top surface of the aforementioned pairs of slots without any adjustment mechanism being provided for varying the height of the rolling platens. As a result, precise dimensional tolerance is required in the forming of the slots in the sides of the carriage to achieve an OCR image. Manufacturing an imprinter with components having precise dimensional tolerances adds to its expense.
In order to obtain a high quality imprint which is OCR readable, it is necessary that a set range of clearance exist between the rolling platens and the base of the imprinter during imprinting. The wheels which support the carriage on the rails of the base must be adjusted to be spaced from each other within a set range so that unacceptable play orthogonal to the flatbed of the imprinter during imprinting does not exist, which would degrade the quality of the imprint, before the clearance between the rolling platens and flatbed can be set.